1. Field of the Invention
The present invention relates generally to a wireless communication system, and in particular, to an authentication method between a mobile node (MN) and a home agent (HA) in a wireless communication system supporting packet communication.
2. Description of the Related Art
With the development of a communication technology, research has been carried out on several technologies for combining a packet-based network (hereinafter, referred to as a “packet network”) using an Internet protocol (IP) with a wireless communication network. One of the more widely known technologies is a CDMA (Code Division Multiple Access) technology. The CDMA system transmits voice or data received from a wireless communication network to a packet-based IP network using an IP packet, so that the packet is finally received at a mobile node (or a mobile host) having an IP address.
An IMT-2000 (International Mobile Telecommunication-2000) system, a typical CDMA system, is a 3rd generation wireless communication system that proposes to enable a user with one mobile node to enjoy a communication service anyplace in the world by integrating various mobile communication specifications separately operated by the respective countries. In the IMT-2000 system, a user can simultaneously access several services through one mobile node. For example, the user may attend a videoconference, while accessing graphic information over the Internet/Intranet, exchanging a multimedia e-mail, and transmitting data files. In addition, the IMT-2000 system provides global roaming service, wireless video service, remote videoconference service, bi-directional entertainment service, etc.
In a wireless communication system supporting packet communication such as the IMT-2000 system, in order for a mobile node to be provided with a packet call service through a packet network, the mobile node requires a unique address so that the packet network may identify the mobile node. This address serves as an IP address in an IP network. It is preferable that the mobile nodes have their own unique IP addresses. However, since the number of available IP addresses is limited, research has been carried out on a system for temporarily assigning an IP address only when the user uses the service. This is called a “Mobile IP” system.
In a wireless communication system supporting the Mobile IP (e.g., 3G packet network), network elements capable of assigning IP addresses to mobile nodes include two Internet access gateways: one is a packet data service node (PDSN, or a foreign agent (FA)) and another is a home agent (HA). The PDSN assigns an IP address to a mobile node requesting a Simple IP service, while the HA assigns an IP address to a mobile node requesting a Mobile IP service. An IP address assigned by the PDSN is deleted after termination of the service, whereas an IP address assigned by the HA is constantly used unless the mobile node moves to a region of another HA.
Meanwhile, IETF (Internet Engineering Task Force) RFC (Recommendation for Comments)-2002, the IP mobility support standard, defines FA-HA authentication for safe communication between the PDSN (FA) and the HA. The FA-HA authentication is positively necessary since the HA may be exposed to a DoS (Denial of Service) attack if a communication region between the FA and the HA is not protected. The FA-HA authentication defined by the RFC-2002 cannot be used in the CDMA wireless communication system. This is because the FA cannot actually share an FA-HA authentication shared key with a plurality of HAs connected to a public network. That is, this is because as the number of HAs and FAs increases, the number of the FA-HA authentication shared keys that one FA or HA should have also increase. Therefore, a method of using a separate IPSec (IP Security) protocol instead of the FA-HA authentication defined by the RFC-2002, or constructing a Virtual Private Network tunnel is considered as the FA-HA authentication method.
According to the IPSec considered for the FA-HA authentication in the wireless communication system supporting packet communication, authentication information is added to a transmission message and then encrypted in order to safely transmit the message. To this end, both sides (HA and FA) transmitting and receiving the message should have information needed for authentication and encryption. That is, the HA and FA should have information on an algorithm to be used for the authentication and the encryption, information on a key to be used for the authentication and the encryption, and information on a valid lifetime of the key. Such information may be previously shared by the HA and FA, but the information is required to be subject to a periodic change for security. To this end, in the case of the IPSec, the HA and the FA exchange the above-stated information using an IKE (Internet Key Exchange) protocol, and change the information periodically. The use of the IKE causes generation of IPSec security association (hereinafter referred to as “IPSec SA”).
The use of the IKE is divided into two steps. A first step is to make a tunnel through which messages for generating an SA to be used for actual data protection are safely transmitted. That is, the first step is an operation of securing safe transmission of messages for generating the IPSec SA rather than actual user data. A second step is a process of making an IPSec SA to be used in maintaining security of the actual data through the IPSec SA made in the first step. The steps are achieved through several message exchanges. In the first step, message exchanges occur from a minimum of 3 times to a maximum of 6 times according to the message exchange method. For example, when main mode that should perform the message exchange six times is selected, an exchange of such messages as HDR, SA, KE, NI, Nr, HDR*, IDii, IDir, HASH_i and HASH_R is required between an initiator (transmitter) and a responder (receiver). Herein, HDR represents a header, SA represents a security association, KE represents a key exchange, NI represents a notice payload initiate, Nr represents a notice payload response, HDR* represents an encrypted header, IDii represents an identification payload initiate, IDir represents an identification payload response, HASH_i represents a HASH payload initiate, and HASH_R represents a HASH payload response. The second step is achieved through 3 message exchanges.
When the IPSec SA is generated, the FA and the HA protect transmission data through authentication and encryption as negotiated in the above steps. An algorithm used at this time consumes process power of the FA and the HA. Therefore, in most cases, the IPSec is constructed by software rather than hardware.
As described above, when the wireless communication system supporting packet communication secures a communication region between the FA and the HA using the IPSec, it requires an additional pre-setup message, causing a considerable increase in a processing load of the FA and the HA due to complexity of the encryption.